are recovered near the town of Trat, 45 km east of Chanthaburi
are common among other minerals in the heavy fraction. The gem-bearing alluvium occurs near the surface or is buried under a sequence of sandy-clay and red-brown clay deposits at depths of a few meters to 10 m.
Along the basalt plateau of Bo Rai, for a distance of 27 km, there are 23 ruby
placer operations, which use mechanical methods with bulldozer stripping and hydraulic washing of the productive layer to recover gem minerals.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 66